On the application of copper foil in the printed circuit board, the conventional process includes the electrochemical deposition of copper sulfate electrolyte on the copper drum surface of the cathode to electroplate copper on the original foil, then through the after-treatment process to procure the ultimate goal product. The surface roughening treatment of copper foil is achieved with hot pressing or calendering metal sheet, copper or nickel, resulted copper foil is used as the base material for laminating with a high glass transition temperature (Tg) epoxy resin substrate, phenolic resin substrate, or polyimide resin substrate into a copper clad laminate (CCL) in electrical and electronic industries.
The basic feature required for surface roughening treated copper foil for printed circuit boards is excellent sufficient peeling strength between copper foil and a variety of epoxy, phenolic, or polyimide resin substrate, and peeling strength will be maintained above the standard in the hot pressing and the various follow-up treatment processes.
Therefore, besides this copper should have excellent acid or alkali chemical resistance, heat resistance and other features, in the formation of circuit patterns made of copper plate etching process, the residue should not cause the deckle edge phenomenon for the excellent etching characteristics. To enable copper foil with a variety of above-mentioned characteristics, usually at first the so-called copper surface roughening treatment is conducted, then the known post-treatment processes including heat resistant layer, rust free layer and silane coupling agent layer are followed up.
In recent years, with notebook computers, mobile phones popularity, the use of the high glass transition temperature (Tg) epoxy printed circuit substrate tends to increase year by year, as compared to the traditionally used FR-4 substrate, peeling strength between the copper foil substrate and the high Tg substrate significantly is lower. To enhance peeling strength between copper foil and the high Tg substrate, generally the surface roughness of copper foil should be improved to overcome the drawack. However, this surface roughening method can easily induce copper powder out of place (powder dropping), and abnormal copper etching residues.
On the other hand, due to high density, high performance and miniaturization trend of electronic components, the circuit of printed circuit boards tends to have high density, the circuit line width is also to the direction of miniaturization. Therefore, copper foil used in printed circuit boards also has the low roughness feature for applying to high density and fine circuit lines. However, lamination peeling strength between this low-roughness copper foil and the circuit board will deteriorate, and the above requirements for copper foil properties will not be able to reach, resulting in the occurrence of contradictory conditions.
In order to have a low roughness on the one hand, meanwhile maintaining the characteristics of copper foil for the requirements needed, in the publicly known existing technology: the Cu—Ni binary alloy system shows better heat resistant peeling strength and salt acid resistance, but it can not be etched with a alkaline etching solution, as revealed in Japanese Patent Application No-1977-145769 and Japanese Patent Application No-1980-058502; Cu—Co system as shown in Japanese Patent Application No. 1983-028893 and Japanese Patent Application No. 1990-292895 with CuCl2 can also be etched in the alkaline etching solution, but heat resistance, peeling strength and salt acid resistance worse than those of Cu—Ni system; Cu—Ni—Co system of Japanese Patent Application No. 1990-292894, Japanese Patent Application No. 1996-236930 reveals a the roughening procession method with an acid copper plating solution containing chromium and tungsten metal ions and one or more metal ion chosen from vanadium, nickel, iron, cobalt, zinc and molybdenum; Japanese Patent Application No. 1999-256389 discloses a roughening procession method with an acidic electroplating solution containing a metal ion selected from molybdenum, iron, nickel or tungsten; and to overcome the poor heat resistant peeling strength, actually arsenic, antimony, bismuth or selenium and other acidic copper electrolyte solution are used for more effective copper roughening treatments (Japan Patent No. 1979-38053, Japan Patent No. 1978-39327), but arsenic, antimony, bismuth and other elements added electrolyte solution results in wastewater treatment and environmental protection problems. However, the known knowledge can only solve part of the copper foil characteristics is problems, but can not fully take into account the requirements of environmental protection and maintain the copper foil peeling strength, heat resistance, acid resistance, moisture resistance, powder dropping and etching characteristics.